It is believed that over the next few decades many of the currently used power sources, such as internal combustion engines in automobiles will be replaced by polymer electrolyte membrane fuel cells (PEMFC's). In order to make these technologies cost effective, and also to meet recycling and reuse standards such as those set by the European Union for vehicle waste, recycling and reuse of the fuel cell materials is essential. (Handley et al., 2002).
Conventional technologies for platinum group metal (PGM) recovery are based on acid dissolution of the PGMs, or a high temperature melt alloying process. The temperatures used sometimes exceed 2000° C. and the methods are thus energy intensive. The above process is most widely applied in the recycling of precious metals from internal combustion engine exhaust gas catalytic converters (Barnes et al, Chemistry and Industry 151, (Mar. 6, 1982); Benson et al., Resources, Conservation and Recycling, 31,1, (2000); Bhakta J. Met., 36 (February, 1994); Hageluken Metall, 55, 104 (March, 2001); Hoffmann Journal of Metals, 40 (June, 1988); Wernick et al., Ann. Rev. Energy Environ., 23, 465, (1998)). Although this recycling technology may be applicable to the recycling of certain fuel processor catalytic components, it is ill suited for PGM recovery from catalyst coated membranes (CCM).
Perfluorosulfonic acid polymer (PFSA) membranes are the most frequently used membrane in the PEM fuel cells. Commercially available polymers include NAFION® marketed by Dupont. The presence of the PFSA, which results in contamination of the high temperature furnace equipment unless expensive HF scrubbing equipment is added, is a major technical limitation in the recycling and reuse of the fuel cell materials. In fact one of the largest reactors in the U.S. is located in the Engelhard facility and is capable of handling at most 10 lbs/hour of perfluoronated polymer material. In Japan the largest PGM recycling facility operated by Tanaka for recycling is based on the Rose process, which cannot tolerate the presence of any F containing material. Regarding hydrometallurgy, the presence of the PFSA™ may block access of the reagent to the Pt sites, thus resulting in poor yields of metal recovery.
Recycling of used perfluorosulfonic acid membranes such as NAFION® from the Chlor-alkali industry also represents a significant source of low cost polymer at the current time. In fact several 10's of thousands of kilograms are sent to landfills annually. The recovery of these materials would allow for a lower cost source of polymer than is currently available.